Loop alembic animation
Related:

reverse alembic
start alembic at specific frame


Once you imported an Alembic Cache, the object in Blender will have an Alembic Cache Constraint.

Check Override Frame.
In the frame property you can set keyframes. The following expression will loop through frame 1, 2, 3, 4. Directly enter the following in the Frame property:
#(frame - 1) % 4 + 1


The Values used in the Python Expression
#(frame - &lt;starting_frame&gt;) % &lt;animation_duration&gt; + &lt;starting_frame&gt;

frame               the actual frame played
starting_frame      the frame id where the animation begins
animation_duration  the number of frames the animation lasts

To customize the driver to your needs, replace starting_frame and animation_duration with your values:
The animation starts at frame 1 and lasts 4 frames: #(frame - 1) % 4 + 1